1. Field of the Invention
The present invention relates to an optical pickup device for writing and reading information on and from a recording medium by emitting light to the optical recording medium.
2. Description of the Related Art
A typical optical pickup device is for writing and reading information on and from an optical recording medium in a non-contact manner. The optical pickup device is adopted in compact disk players (CDPs), CR-ROM drives, digital versatile disk players (DVDs) and DVD-ROMs.
FIG. 1 shows the optical arrangement of an optical pickup device manufactured by Sony, a Japanese corporation, as an example of the conventional technology. Referring to the drawing, an optical pickup device includes a light source 10, an objective lens 13 for focusing a main light ray emitted from the light source 10 and branched at a beam splitter 11 in one direction at an optical disk 1, a main photodetector 15 for receiving a light ray reflected by the optical disk 1 and passing the beam splitter 11, and a monitoring photodetector 17 for receiving a sub-light ray branched at the beam splitter 11 in another direction. A collimating lens 12 for focusing an incident light is disposed on an optical path between the beam splitter 11 and the objective lens 13. Also, a holographic optical element 14 for diffracting and transmitting an incident light is installed on the optical path between the beam splitter 11 and the main photodetector 15.
The main photodetector 15 reproduces the input light as a signal. The reproduced signal is determined in proportion to the amount of change in the amount of light output from the light source 10. Thus, to obtain a reproduced signal of high quality, the amount of output light must be maintained constantly. For this purpose, the monitoring photodetector 17 detects the amount of sub-light which is not reflected by the beam splitter 11 and passes through it without change. The information on the detected amount of sub-light is used for control of the amount of output light of the light source 10.
However, in the conventional optical pickup device, the light emitted from the light source 10 diverges at a predetermined angle after being branched at the beam splitter 11 whereas the size of a surface for detecting light of the monitoring photodetector 17 where the divergent light is detected is limited. Thus, the monitoring photodetector 17 cannot detect an amount of sub-light enough to obtain information to effectively control the output light of the light source 10.
To solve the above problems, it is an objective of the present invention to provide an optical pickup device having an improved structure by which the light emitted from a light source is focused to proceed to a monitoring photodetector.
Accordingly, to achieve the above objective, there is provided an optical pickup device which comprises a light source for emitting light, a beam splitter installed on an optical path of the light emitted from the light source for splitting the light, an objective lens for focusing a main light split by the beam splitter at an optical disk, a monitoring photodetector for receiving a sub-light split by the beam splitter and monitoring the amount of light output from the light source, a main photodetector for receiving the light emitted from the light source and reflected by the optical disk and passing through the beam splitter and detecting an error signal and an information signal, and a collimating lens installed on the optical path between the light source and the beam splitter for condensing both the main light and sub-light split by the beam splitter, so that the amount of light received by the monitoring photodetector increases.
It is preferred in the present invention that a radiation angle of the main light and sub-light passing through the collimating lens is 4xc2x0-6xc2x0, preferably, 5xc2x0.
Also, it is preferred in the present invention that the optical pickup device further comprises a collimating lens, installed between the beam splitter and the optical recording medium, for condensing the main light passing through the beam splitter.
According to another aspect of the present invention, there is provided an optical pickup device which comprises a first light source module for emitting first light having a predetermined wavelength, a second light source module for emitting second light having a wavelength different from that of the first light, a first beam splitter for changing a proceeding path of the first light emitted from the first light source module, a second beam splitter for splitting the second light emitted from the second light source module into a main light and a sub-light and transmitting the first light, an objective lens for focusing the main light split by the second beam splitter and the first light on an optical recording medium, a main photodetector for receiving the light emitted from each of the light source modules, reflected by the optical recording medium, and passing through the beam splitters, and detecting an error signal and an information signal, a monitoring photodetector for receiving the sub-light split by the second beam splitter and monitoring the amount of light output from the second light source module, and a first collimating lens installed on the optical path between the second light source module and the second beam splitter for condensing both the main light and the sub-light split by the second beam splitter by a predetermined angle.
It is preferred in the present invention that the optical pickup device further comprises a second collimating lens installed on the optical path between the second beam splitter and the objective lens for condensing the main light and the first light proceeding toward the objective lens.
Also, it is preferred in the present invention that the first collimating lens condenses the incident second light by a radiation angle of 5xc2x0.